Apparatus for debarking logs individually

ABSTRACT

The invention relates to an apparatus for debarking logs individually with the aid of high-pressure water jets. The spray nozzles are intended to spray water in focused jets against the log at the same time as the log moves past the spray nozzles. The invention is characterized by a ring (22) through which the log is intended to be fed, in that units (42, 46, 46&#39;) are mounted on the inside of the ring, uniformly distributed about the periphery of the said ring, which units are intended to bear against the surface of the log passing through the ring, in that a spray nozzle (40) is arranged in each such unit, which spray nozzle is made to maintain an essentially constant distance from the surface of the log by means of the fact that the unit bears against the surface of the log, this distance lying within a range of distance from the surface of the log which is optimal for debarking. In addition, suitable means are intended to turn the ring in an oscillating manner to and from about the centre axis of the ring during debarking.

TECHNICAL FIELD

The invention relates to an apparatus for debarking logs individuallywith the aid of high-pressure water jets, the apparatus comprising anumber of spray nozzles intended to spray water in focused jets onto thelog at the same time as the log moves past the spray nozzles.

PRIOR ART

Before cutting up the raw materials of wood in saw mills and the pulpindustry, it is necessary to remove the bark from the logs. Two methodsare mainly used for this purpose, these methods having their originsaround the periods when these respective industries came into being.

Saw mills mainly use so-called Cambio debarking in which the bark ispeeled off with the aid of knives which rotate around the log in anannular holder. This method leaves some of the bark remaining on thetree-trunk and is in addition energy-intensive and noisy. The equipmentalso requires careful servicing.

The pulp industry uses debarking drums with diameters of 3-6 m andlengths of up to 35 m. The drum lies at a slight incline, mounted onpulley brackets and is set in rotation by drive machinery. The logs arefed in at the upper end, and, as a result of the rotation andinclination of the drum, the logs are conveyed through the drum andeventually issue at the other end. The debarking is achieved by means ofthe logs scraping and striking against the walls of the drum and againstother logs in the drum. A virtually one hundred percent debarking resultis sought so as to ensure that residual bark does not impair the qualityof the paper. This means that the dwell time in the debarking drum isdetermined by the logs which are most difficult to debark. This in turnmeans that most of the logs have too long a dwell time in the drum,which leads unnecessarily to a high energy expenditure. In the debarkingdrums the logs are sprayed continuously with water, which is required as"lubrication". Water is also used as a means for conveying the barkwhich has been peeled off. These large amounts of water have to be dealtwith and cleaned at a later stage. This debarking method thus uses uplarge amounts of energy and water, and at the same time the debarkingequipment is expensive and takes up a great deal of space.

Debarking with high-pressure water has also been proposed. As early as1912 a Swedish patent 35392 was published relating to a method fordebarking wood, in which "the wood is made to execute a spirallingmovement past a pressure-medium jet, where appropriate provided withsolid particles".

An American patent U.S. Pat. No. 2,463,084 from 1949 relates todebarking with high-velocity jets, in which the unit which comprises thespray nozzles moves around the log, so that the debarking is executed ina spiral as the log moves through the rotating instrument.

Another American patent U.S. Pat. No. 2,473,461 stresses the importanceof the jets being directed radially with respect to the axis of the logat all times, regardless of the size and shape of the log, and of thespray nozzles being located at a predetermined optimal distance from thesurface of the log. However, the apparatus which is described in thepatent specification cannot satisfy the stated conditions in practiceand it is additionally complicated and, in quite general terms,functionally unreliable.

The principle of using high-pressure water for debarking logs hastherefore not as yet been applied in practice.

BRIEF DISCLOSURE OF THE INVENTION

The present invention has the object of providing an improved apparatusof the type which is mentioned in the introduction above. A particularobject of the invention is to offer an apparatus for debarking logsindividually with high pressure water which is sprayed against the log,requiring considerably less water, energy, space and maintenancecompared with the abovementioned debarking apparatuses which aregenerally used in the forest industry at present.

The present invention also aims to offer a debarking apparatus in whichthe spray nozzle is held essentially within an optimal range of distancefrom the surface of the log, so that the focused jet cuts through thelayer of bark, after which the jets of water are broken up on the woodlying within the bark, the said bark shattering and falling off.

These and other objects of the invention can be achieved by virtue ofthe fact that the invention is characterized by what emerges from thepatent claims which follow.

Further characteristics and aspects of the invention emerge from thefollowing description of a preferred embodiment.

BRIEF DESCRIPTION OF THE FIGURES

In the following description of a preferred embodiment reference will bemade to the attached drawings in which:

FIG. 1 shows diagrammatically a debarking station in which the apparatusaccording to the invention can be used,

FIG. 2 shows the debarking apparatus in longitudinal section, with twospray nozzles and a log in the process of being debarked,

FIG. 3 shows the debarking apparatus in a front view along III--III, and

FIG. 4 shows a bottom view of a component of the debarking apparatus forholding and positioning a spray nozzle.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows diagrammatically a plant in which the apparatus accordingto the invention is included. In the plant the logs first come to areceiving hopper 1, in which the logs are laid on top of one another. Inthe receiving hopper 1 a preliminary debarking takes place as a resultof the logs lying and scraping against one another. From the receivinghopper 1 the logs are advanced on a rolling deck 2, after which asingle-log feeder 3 feeds the logs out one by one onto a conveyor 4which leads to an apparatus 5 for measuring and identifying one log at atime, in which apparatus 5 a computerized measurement system 6, whichcan be of a type known per se and is coupled to a process monitor,optically measures the diameter and straightness of the log which is dueto be measured. According to an alternative of the preferred embodimentthe measurement can also be performed with the aid of laser orultrasound in accordance with known techniques. The presence ofprotruding knots is also revealed during measurement. Finally, themeasurement system 6 classifies the roughness of the bark. When themeasurement in the system 6 has been completed, the log advances to theconveyor 7 where logs which have been found by the measurement system 6to be too crooked, or to have too great a diameter, or to haveprotruding knots, are removed from the conveyor and are thrown down intoa hopper 8. These logs are later used for other purposes. The remaininglogs are moved via a belt conveyor 9 to a debarking apparatus 10according to the invention, where the logs are debarked one by one.

The bark stripped in the debarking apparatus 10 is conveyed to a barkcompressor 11, to which bark also arrives on a conveyor belt 12 from thereceiving hopper 1, the bark having been treated in a shredder 13 inorder to obtain the correct piece thickness.

The debarked log is then conveyed onwards into a forest industryprocessing plant for the production of pulp or saw mill products.

FIGS. 2 and 3 show the structure and function of the debarking apparatus10. The log approved for debarking leaves the conveyor belt 9 and ismoved onwards with the aid of feeding mechanisms 20 into the debarkingapparatus. The feeding mechanisms 20 can consist of feeding mechanismsof the "Cambio" type in accordance with known techniques, the feedingmechanism 20 preferably being used in pairs (not shown) so that one pairis located on the inlet side of the debarking apparatus and one pair islocated on its outlet side, the log being fixed the whole time in thelongitudinal direction.

The debarking apparatus 10 comprises a ring 22 suspended on five wheels24 which are distributed about the periphery of the ring 22 and allowthe ring to be turned about its centre axis. Each one of the wheels 24is located on a projection 26, these projections being connected to aframe. The frame 28 can be raised and lowered by means of a hoist device32 in an outer frame or guide 30 which is formed by a U-shaped profile.The purpose of the hoist device 32 is to raise or lower the debarkingapparatus 10, on the basis of information relating to the diameter ofthe log, so that the centre line of the log coincides closely with thecentre line of the ring 22. According to an alternative of thisembodiment the centre lines of the log and of the ring can be made tocoincide closely by virtue of the fact that the abovementioned feedingmechanisms 20 can be raised or lowered in relation to the debarkingapparatus 10. At the top of the ring 22 a lever 34 projects at rightangles from the ring 22. At its upper end the lever 34 is connectedrotatably to a hydraulic cylinder 36. With the aid of the hydrauliccylinder 36 the ring can be made to rotate in an oscillating mannerabout its centre line.

Four high-pressure nozzles are arranged on the inside of the ring 22,each one mounted on an articulated parallelogram 42 which, by turning atthe four points of articulation, can move inside the ring in a radialplane with respect to the latter. Each one of the four articulatedparallelograms 42 comprises two parallel pairs 43 of mutually parallelbars 44. At their ends the pairs of bars or the arms 43 are rotatablyconnected to projections on the inside of the ring 22. Between the bars44 in each pair of bars or arm 43 there is a transverse bar 48.Extending between these transverse bars 48 is a longitudinal bar 50which is connected rotatably at both its ends to the transverse bars 48.The longitudinal bar 50 is parallel with an imaginary line between theprojections on the inside of the ring 22 in the said radial plane of theparallelogram and forms, together with the said line, the third andfourth arms in the articulated parallelogram 42. Thus, in all thepositions which can obtain by inclining the two parallel pairs of barsor the arms 43, the longitudinal bar 50 is parallel with the centre lineof the ring 22.

The high-pressure nozzles 40 are mounted on the longitudinal bars 50 inthe articulated parallelograms 42, there being located on each suchlongitudinal bar 50 a high-pressure nozzle 40 directed radially towardsthe centre line of the ring 22. Each one of the nozzles 40 is located onan adjustment device 60 by means of which the distance of the nozzlefrom the surface of the log can be adjusted, independently of thesetting of the articulated parallelogram 42, but, rather, on the basisof information such as variety of tree, time of year and the like.

The parallel pairs of bars or the arms 43 are each connected at theirrespective inner ends to a follower 46, 46' which, during debarking, isintended mainly to follow the surface of the log by rolling or slidingon the latter, so that the articulated parallelogram moves in its radialplane by turning at its four points of articulation. In this way thelongitudinal bar 50, on which the high-pressure nozzle 40 is mounted, isat all times held at a substantially constant distance from the surfaceof the log. This in turn ensures that the high-pressure nozzles 40 areat all times located within a range of distance from the surface of thelog which is essentially optimal for debarking, since the position ofthe nozzle 40 relative to the longitudinal bar 50 has been set, as hasbeen mentioned above, with respect to the actual parameters of the typeof wood.

Located at the inlet side of the debarking apparatus, on each pair ofbars or arms 43 parallel to the inlet side, is a first protective plate54 which is formed essentially as a quarter circle and which extendsalmost from the periphery of the log almost to the inside of the ring.Furthermore, a second protective plate 55 is additionally located at theoutlet side of the debarking apparatus, on each one of the arms/pairs ofbars 43 and to the inside of the second follower 46', this secondprotective plate 55 extending outwards a relatively short distancealmost from the periphery of the log.

The followers 46, 46' consist of a hemispherically shaped hollow holder52, in which holder 52 a ball 53 sits which can rotate freely in alldirections. The followers 46, 46' have an attachment for rinse water,which water is intended to prevent dirt from penetrating between theball 53 and the holder 52 by constantly rinsing this intermediate space.In this way a lubrication of the ball 53 is also achieved.

The articulated parallelograms 42 thus follow the contour of the logindividually, that is to say they assume positions which are determinedby the diameter of the log, its curvatures and any small projectingknots on the log, by being pushed away or springing back, by means oftheir rotating at the four corners of the parallelogram, as emerges fromFIG. 2. Each articulated parallelogram 42 is also equipped, for thispurpose, with a spring-mounted hydraulic cylinder 41 which ensures thatat least one of the followers 46, 46' bears at all times against thesurface of the log. It is normally the follower 46 located nearest theinlet which bears against the log during the greater part of thedebarking process, while the follower 46' located nearest the outletadditionally has the purpose of preventing the nozzle 40 from fallingdown onto the log when the rear end of the log has passed the follower46 located nearest the inlet. According to one alternative of thisembodiment, at least the follower 46' can also be designed as a slaywhich follows the surface of the log by sliding thereon.

In order to ensure that the jet 39 of medium will be able to act on thewhole surface of the log, the jet 39, which has an active area of a fewcm², is moved over the surface of the log. This is achieved by using arotating apparatus in accordance with known techniques, in which anozzle 40 is equipped with one or more mouthpieces at a slight angle,which nozzle 40 is set in rotation by the water which flows through it.In this way the stripping surface is increased to 1-2 dm². In order forthe log to be stripped round the whole periphery, it is necessary forone or more nozzles 40 to rotate round the log or for the log to rotatewith respect to the nozzle 40.

According to the present embodiment of the invention, there are fouruniformly distributed nozzles. These nozzles 40 are mounted in theannular stand 22 which is rotated to and fro inside the wheels 24 withthe aid of the hydraulic cylinder 36 while the log is being fed throughthe ring 22, these nozzles 40 thus being able to act on the surface ofthe log within their respective sectors.

After the log has passed the station 5 and the measurement system 6, theoperating parameters of the debarking apparatus 10 are adapted to thediameter of the log and the outer structure of the bark. The operatingparameters are also affected by pre-set basic conditions such as varietyof tree, storage period, preliminary treatment and time of year. Allthese basic conditions dictate how loosely or how firmly the bark lieson the log, and they also affect the thickness of the bark. A furtherbasic operating parameter is the subsequent use of the debarked log. Ifthe log is to be used for the production of light mechanical wood pulp,all the bark must basically be removed. If, on the other hand, the logis to be sawn, the requirements for clean debarking of the log are less.

The term intensity here refers to the period during which an arbitrarypoint on the surface of the log is acted upon by jets 39 of medium andto the prevailing pressure of the medium. The intensity of the debarkingoperation is set on the basis of the following variables, which are inthis case the pressure of the jets 39 of medium, the distance of thenozzle 40 from the surface of the log, the speed of the log in thelongitudinal direction relative to the nozzle 40, and the to and fromovement of the nozzles 40.

These variables have values in the following ranges:

    ______________________________________                                        Pressure of jet of medium                                                                            350-800 bar                                            Distance of nozzle from                                                                               50-150 mm                                             surface of log                                                                Speed of log in         0.1-1 m/s                                             longitudinal direction                                                        Rotation of nozzle about log                                                                          30-200 rpm                                            (to and fro movement                                                          corresponding to a rotational                                                 speed of                                                                      ______________________________________                                    

In order to facilitate the introduction of the log into the spray zoneof the debarking apparatus, the parallelogram moves out to a standbyposition at the periphery between each log. As a result the debarkingapparatus 10 is fully open when the log arrives, and the log does nothave to act on the protective plates 54 and on the followers 46 in orderto force itself into the spray zone of the debarking apparatus. Aphotocell (not shown) indicates when the log arrives, and the photocellemits an impulse, whereupon the hydraulic cylinders allow the followers46 to drop. The impulse travels via the processor, in which account istaken of the speed of the log in the longitudinal direction, this speedhaving been determined upon earlier measurement of the log, and thefollowers 46 always drop and land on the surface of the log immediatelybehind its front end. When the rear end of the log passes the photocell,an impulse is emitted to the processor to the effect that theparallelograms 42 are to return to the standby position at the peripheryafter a certain period of time which is determined by the speed of thelog in the same way as above, the followers 46' leaving the surface ofthe log immediately in front of its rear end. By means of this procedurethe equipment is saved from jolts and fatiguing stresses, and at thesame time fewer demands need be placed on the feeding mechanism due tothe fact that the latter does not have to force the log into the sprayzone.

When the log arrives in the spray zone of the debarking apparatus 10,the medium is sprayed onto the log at a pressure, and at a distancebetween the nozzles 40 and the surface of the log, which is such thatthe focused jet cuts through the layer of bark, after which the jets ofwater break up against the wood lying within the bark, the barkshattering and falling off. It is of the utmost importance that the log40 is at the correct distance from the surface of the log and that thejet has the correct kinetic energy. If the nozzle 40 lies too near thelog, the kinetic energy of the focused jet is too great, the result ofwhich is that the jet penetrates past the bark, and the wood is alsoshattered. If, on the other hand, the nozzle 40 lies too far from thesurface of the log, at a distance beyond the reach of the focused jet,the kinetic energy of the jet will essentially be lost and the jet willbreak up in the air. The optimal distance is set with the aid of theadjustment device 60, which distance is kept essentially constant bymeans of the movements of the articulated parallelogram in the radialplane.

We claim:
 1. An apparatus for debarking a log passed therethrough,comprising:a ring member having a central axis and through which the logis passed; and a plurality of spray units mounted on said ring member,wherein each spray unit comprises: an articulated frame including:firstand second pairs of parallel arms, each arm of said first and secondpairs of parallel arms being pivotably connected at respective firstends thereof to said ring member; and an intermediate arm pivotablyinterconnected with both said first and second pairs of parallel arms;and a spray nozzle mounted on said articulated frame and arranged tospray a water jet against each log passed through said ring member,wherein said spray nozzle is arranged so as to maintain a substantiallyconstant distance from the log.
 2. An apparatus as claimed in claim 1,wherein said ring member is rotatable about said central axis, theapparatus further comprising means for rotatably oscillating said ringmember about said central axis thereof.
 3. An apparatus as claimed inclaim 1, wherein said spray nozzle is mounted on said intermediate arm.4. An apparatus as claimed in claim 1, wherein a radial position of saidspray nozzle can be adjusted.
 5. An apparatus according to claim 1,wherein at least one arm of said first and second pairs of parallel armsis provided with a follower on a second end thereof, opposite said firstend of said at least one arm pivotably connected to said ring member,said follower being constructed and arranged to contact and follow thesurface of the log.
 6. An apparatus according to claim 1, wherein aposition of said ring member is adjustable such that said central axisof said ring member can be made to substantially coincide with an axisof a log being passed therethrough.
 7. An apparatus according to claim1, wherein said arms of said first and second pairs of parallel arms areinterconnected by first and second transverse bars, respectively.
 8. Anapparatus according to claim 7, wherein said intermediate arm ispivotably connected to said first and second transverse bars,respectively.
 9. An apparatus according to claim 5, wherein saidfollower is biased in a radially inward direction, relative to said ringmember.
 10. An apparatus according to claim 1, wherein said first andsecond pairs of parallel arms are oriented relative to one another alonga direction parallel to said central axis of said ring member.
 11. Anapparatus according to claim 1, wherein four said spray units aremounted on said ring member.
 12. An apparatus according to claim 1,wherein said plurality of spray units are constructed and arranged to beselectively movable.
 13. An apparatus according to claim 12, whereinsaid plurality of spray units are selectively movable in a radialdirection relative to said ring member.
 14. An apparatus according toclaim 13, further comprising means for controlling said selectivemovement of said plurality of spray units.
 15. An apparatus according toclaim 14, wherein said means for controlling is operable to cause saidplurality of spray units to move inwardly and outwardly incorrespondence with the passing of the log through the ring member. 16.An apparatus according to claim 1, wherein said plurality of spray unitsmounted on said ring member are located at regular intervalstherearound.